1. Field of the Invention
The present invention relates generally to devices for transmitting torque wherein is included means for indicating the transmission of torque in excess of a predetermined value. The present invention relates more particularly to the provision of such devices in lever operated hoists.
2. Description of the Prior Art
Proper mechanical design of lever operated hoists and other devices employing a rotary mechanical input require limitation of the loads carried by the devices. To allow the devices to function for their entire design life, overloading above a rated value should be either prevented entirely or should be limited to occasional occurrence by indicating to the user that an overload is present so that continuous or repetitive loading at this level may be avoided. Devices for limiting the load capacity of or for indicating the existence of an operating overload in lever operated hoists are therefore well known in the prior art. The prior art devices, however, have certain major disadvantages. One of these disadvantages can be seen in devices which limit the load to be moved by use of a regulator such as is described in U.S. Pat. No. 3,776,514 to Eggleton, Jr. et al. A large number of relatively complex parts are employed to accomplish the overload prevention function, the successfully consistent operation of which is dependent upon frictional forces between brake parts.
Another disadvantage of the prior art hoists may be seen in the type which indicate the existence of an overload through deflection of the outer end of the input drive lever handle such as that disclosed in U.S. Pat. No. 3,772,316 to Hawkins et al. Hoists of this type readily lend themselves to abuse, since tubular extensions which engage the input lever inboard of its indicating portion may be used by operators to increase their mechanical advantage. This practice, which is a common mechanical expedient, both increases the likelihood of overload and prevents operation of the mechanism intended to indicate the existence of the overload.